we allow all users to create their own blogs, we have a class attached to the event hander that updates the blog owner to the user that created the blog. Our problem is that this gives the users access to Manage Blog Theme in the new control panel. I've tried removing the manage blog theme access in the owners group, but this doesn't seem to remove this option. We are running ver 10.0.3.6288.
Unfortunately, the owner of the blog automatically gets permission to manage the theme by being named the owner of the blog. Unfortunately, this is not configurable as its a shortcut in effective permission calculation.
The work-around may not work for your site if you have a lot of users, but would consist of not setting the user as the owner but creating a role for each blog that grants only the appropriate permissions to the user who otherwise "owns" the blog.